It is well known that some ferroelectric materials exhibit dielectric, piezoelectric, electrorestrictive, pyroelectric and electro-optic properties that may be useful for nanoscale devices, including memory devices and electro optical devices. Ferroelectric materials are characterized by spontaneous and remnant polarization and hysteresis in the polarization, which give rise to some of these properties. For example, polarization in ferroelectric materials may be effected by subjecting them to an electric field.
This change in polarization may be used for storing binary information, or in optical devices, changes in polarization may give rise to changes in the refractive index of the material.
Planar film ferroelectrics have undergone a significant amount of research for use in electronics, memory and electro optical applications. This research has been focused in large part on their use in thin-film ferroelectric capacitors. In some cases, planar film ferroelectrics have been explored for making random access memory (RAM), field effect transistor (FET), and electro optical devices. In general, planar film ferroelectrics suffer from a lack of scalability, leakage, large power consumption and volatility in their application.
The depolarizing field within ferroelectric materials that arises from incomplete screening is known to be principal source of ferroelectric instability in thin films and nanostructures. The depolarizing field is believed to give rise to an evolution of ferroelectric polarization P and ferroelectric phase transition temperature T with finite size. Although reducing film thickness may decrease polarization, reduced film thickness poses significant difficulty for retaining memory storage capacity. Reduced film thicknesses have also given rise to problems in memory storage devices associated with current leakage, power consumption and non-volatile operation.
Thus, there remains a need for ferroelectric devices with increased scalability, low leakage, low power consumption and non-volatile operation.